This invention relates in general to an electronic switch and, more particularly, to an electronic switch in which one or more signal terminals can be selectively coupled to a further terminal.
A known type of electronic switch circuit has two or more signal terminals, each of which is coupled to the same common terminal through a respective switching transistor. One application for a switch of this type is to effect switching of high power radio frequency (RF) signals in a cellular telephone. In a switch of this type, each switch transistor should provide low insertion loss when it is on, and high isolation when it is off. Trying to optimize both features can involve competing considerations. As one aspect of this, if a transistor is coupled to a signal terminal which in turn is coupled to circuitry with a low load impedance, maintaining high isolation while the transistor is off can be problematic.
Also, it is possible in a switch circuit of this type to increase the sizes of the switch transistors in order to increase the current and power handling capability of the switch circuit. Increasing the size of a switch transistor tends to reduce its insertion loss when it is on, but also tends to degrade the isolation which it provides when it is off, especially where its signal terminal is coupled to circuitry with a low load impedance. In a switch circuit of the type being discussed here, degradation in the isolation of a switch transistor which is off can act to degrade the insertion loss of another switch transistor which is on.
From the foregoing, it may be appreciated that a need has arisen for a method and apparatus for effecting electronic switching in a manner which facilitates both low insertion loss and high isolation. One form of the invention includes an apparatus that involves: first and second terminals; a first electronic switch coupled between the first and second terminals, the first electronic switch having a first control input; and a capacitor and a second electronic switch coupled in series between the first control input and a reference voltage, the second electronic switch having a second control input.
A different form of the invention includes an apparatus that involves: first, second and third terminals; first and second electronic switches coupled in series between the first and second terminals, the first electronic switch having a first control input and the second electronic switch having a second control input, and the third terminal being coupled to a node between the first and second electronic switches; a first capacitor and a third electronic switch coupled in series between the first control input and a reference voltage, the third electronic switch having a third control input; and a second capacitor and a fourth electronic switch coupled in series between the second control input and a reference voltage, the fourth electronic switch having a fourth control input.
Yet another form of the invention includes a method of controlling a circuit having a first electronic switch which is coupled between first and second terminals, and which has a first control input, where the method involves: providing a second electronic switch and a capacitor in series between the first control input and a reference voltage, the second electronic switch having a second control input; and selectively applying control voltages to each of the first and second control inputs.
Still another form of the invention includes a method of controlling a circuit having first and second electronic switches coupled in series between first and second terminals, and having a third terminal coupled to a node between the first and second electronic switches, the first and second electronic switches respectively having first and second control inputs, where the method includes: providing a third electronic switch and a first capacitor which are coupled in series between the first control input and a reference voltage; providing a fourth electronic switch and a second capacitor which are coupled in series between the second control input and a reference voltage; and selectively applying control voltages to each of the first, second, third and fourth control inputs.